1. Field of the Invention
The present invention relates to a frequency divider; more particularly, the invention relates to a low-noise frequency divider dividing the high frequency of a clock by 2K.
2. Descriptions of the Related Art
Frequency dividers are widely applied in many fields. For example, in radio frequency (RF) transceivers, a TX RF low band requires a frequency divider to divide the frequency of a clock by four, while a TX RF high band requires a frequency divider divide the frequency of a clock by two. In addition, a RX low band requires a frequency divider to divide the frequency of a clock by four and output four quadrature signals.
Operation frequencies of the TX and RX modes differ by 20 mega Hz (20 MHz), therefore the TX mode is designed to have a lower phase noise at 20 MHz. There are two conventional designs of frequency dividers. One is the dynamic frequency divider, which has a low phase noise, but cannot deal with a high frequency clock. The other frequency divider is a source-coupled-logic (SCL) frequency divider, which can tolerate high frequency clicks, but lacks phase noise integrity.
U.S. Pat. No. 6,130,564 discloses a frequency divider with two inputs and one output. Even though the frequency divider performs a high frequency divider circuit, the frequency divider cannot perform a rail-to-rail swing range; therefore, the frequency divider may function incorrectly due to an indistinguishable signal caused by the non-rail-to-rail swing range.
The paper “A quad-bad GSM-GPRS transmitter with digital auto-calibration” presented in the 2004 JSSC discloses a frequency divider that applies charge sharing principles with the inverter-combined-transmission gate circuitry to achieve frequency dividing. However, due to resistance-like characters of the transmission gate, the charge flowing through the transmission gate cannot flow too quickly. Thus, the frequency divider cannot tolerate high frequency.
As a result, a low-noise frequency divider that divides the high frequency of a clock by 2K is needed in the communication industry.